During engine operation, the reciprocating action of a pump diaphragm sucks fuel through the inlet line to the pump in the fuel tank and forces the fuel through the discharge line of the pump into a carburetor. The fuel in the line between the pump and the fuel tank consists substantially of a long column of liquid having an inertia which must be overcome when the diaphragm sucks the fuel through the inlet line and which must be resisted when the fuel in the inlet line is suddenly stopped by the closing of the inlet valve each time the pump starts a pumping stroke. Also, the fuel in the outlet line of the pump extending to the carburetor contains a column of fuel which is moved rapidly outwardly and then stopped with the closing of the outlet valve each time the diaphragm reverses and provides a suction stroke. The inertia of the fuel in the outlet column must be overcome upon each movement of the fuel into the pumping chamber and upon the stopping of the fuel flow each time the discharge valve closes.
The pump diaphragm of a fuel pump in an automotive vehicle may reciprocate up to around 2,000 strokes a minute. At high speed the inlet valve and the discharge valve are opened and closed at substantially the same rate and it has been found that with an engine operating at such high speed, the inlet and discharge valves of the pump oftentimes do not operate efficiently at such a high pumping rate. Therefore, pulsation chambers or vapor domes have been provided heretofore to dampen the rapid pulsations of the pump so that the fuel is moved at an even rate through the inlet and outlet conduits and only the fuel adjacent the inlet and discharge valves of the pump is reciprocated at or upon each pumping stroke. By evening the fuel flow, a higher fuel flow through the fuel pump may be obtained.